The ability to generate normal Ca2+ transients in response to spermatozoa develops during the final stages of oocyte growth and maturation

Intracellular Ca2+ oscillations at fertilization are responsible for trigge ring egg activation. The aim of this study was to examine the effect of the age of the oocyte donor and in-vitro maturation on the generation of Ca2transients at fertilization. The results show that <10% of in-vivo and in-v itro matured oocytes from 19-day old mice develop to the blastocyst stage i n vitro. In contrast, 43% of in-vivo and 25% of in-vitro matured oocytes fr om 24-day old mice developed to the blastocyst stage. In parallel experimen ts, intracellular Ca2+ was monitored at fertilization. Oocytes from 19-day old mice generate significantlyfewer transients than oocytes from 24-day ol d mice. In-vitro maturation significantly decreased the ability of oocytes from 19-day old mice but not 24-day old mice to generate Ca2+ transients in response to spermatozoa. Furthermore, we investigated the effect of oocyte maturation on Ca2+ signalling. Immature oocytes generated fewer Ca2+ oscil lations and ceased oscillating earlier than mature oocytes. These studies s uggest that the ability to generate Ca2+ transients in response to spermato zoa increases in the final stages of oocyte development and during oocyte m aturation. This may contribute to the acquisition of developmental competen ce in the final stages of oogenesis.